In this work, we report on a significant breakthrough in fabricating the critical tunnel oxide layer of tunnel oxide passivated contacts (TOPCon) high-efficiency solar cells compatible with high-volume manufacturing. We show that the tunnel oxide can be controlled at the atomic scale, enabled by an innovative tube-type industrial plasmaassisted atomic layer deposition (PEALD) method. In combination with an in situ doped poly-Si (n + ) layer grown by plasma-enhanced chemical vapor deposition, a uniform, ultrathin $1.3 nm SiO x layer is obtained at the c-Si/SiO x /poly-Si (n + ) interface.Extremely low recombination current densities down to 2.8 fA/cm 2 and an implied open-circuit voltage (iV oc ) as high as 759 mV are achieved, comparable to state-ofthe-art laboratory results. The developed tube-type PEALD SiO x is applied to industrial TOPCon solar cells resulting in a solar cell efficiency and open-circuit voltage of up to 24.2% and 710 mV, respectively. The tunnel oxide process window is about 2.4 Å, highlighting the importance of precisely controlling the tunnel oxide thickness at the atomic scale for TOPCon solar cells. The newly developed tube-type industrial PEALD SiO x method opens up a promising new route toward mass production of high-efficiency industrial TOPCon solar cells. Furthermore, the developed tube-type PEALD method can easily be integrated with the industrial tube-type plasmaenhanced chemical vapor deposition (PECVD) method, thus enabling the deposition of all thin film layers in TOPCon solar cells in one integrated PEALD/PECVD system. This significantly simplifies manufacturing complexity and fosters the commercialization of next-generation high-efficiency industrial TOPCon solar cells.
In this work, single-side aluminum oxide (Al 2 O 3 ) deposition enabled by a new tubetype industrial plasma-assisted atomic layer deposition (PEALD) technique is presented to meet the increasingly stringent requirements for high-efficiency solar cell mass production. Extremely low emitter saturation current densities, J 0e , down to 15 fA/cm 2 are achieved on an industrial textured boron emitter with a sheet resistance of 104 Ω/sq, passivated by PEALD Al 2 O 3 /PECVD SiN x stack after firing. An implied open-circuit voltage of up to 721 mV is obtained on symmetrical lifetime samples. The underlying passivation mechanisms of this new tube-type PEALD Al 2 O 3 are investigated by contactless corona-voltage measurements. The results indicatethat the superior passivation is mainly attributed to a low interface defect density down to 1.1 Â 10 11 cm À2 eV À1 and a high negative fixed charge density up to 4.5 Â 10 12 cm À2 . Simulations show that the obtained J 0e is close to its intrinsic limit.Lastly, the developed tube-type PEALD Al 2 O 3 is applied to industrial TOPCon solar cells achieving an average cell efficiency above 24% and a maximum V oc of 707 mV.This work shows that the record level of surface passivation available from lab-scale PEALD reactors is now available in a flexible high-throughput industrial PEALD platform, which opens a new route for mass production of high-efficiency industrial TOPCon solar cells with a lean process at low costs.
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